As described in one of the inventor's patents, U.S. Pat. No. 4,501,185, electromagnetic pickups are used with stringed musical instruments, such as electric guitars, to convert the vibrations of "picked" strings into electrical signals for subsequent amplification into sound. The pickups usually comprise a magnet system, including one or more permanent magnet elements and pole pieces, to establish a magnetic field within which the strings vibrate, and coils wound on bobbins disposed in the field to generate electrical signals corresponding to flux variations in the field due to the strings' vibrations. These electrical signals are amplified into musical sounds by circuits and equipment well-known in the trade.
Typically, the pole pieces of a pickup are situated through the bobbins and the pickup itself is generally mounted on the face of the instrument below the strings. The coils for developing the electrical signals are wound on bobbins arranged so that the pole pieces are within the coils to allow the magnetic field developed by the magnet and pole pieces to envelope the coil. Each string, when set into motion, causes variations in the magnetic field in the vicinity of the pole piece or pieces and the variations are converted into electrical signals by the interaction of the magnetic field with the coil.
One particular type of an electromagnetic pickup is the single-coil arrangement. As the instrument's strings vibrate, the single coil senses the magnetic field variations and converts those variations to electrical signals. This type of pickup has a disadvantage in that an audible hum is created when the coil senses interference caused by radiating electromagnetic generating sources. For example, the single coil tends to pick up 60 cycle signals emanating from the power supply used in the amplification equipment as well as from other environmental sources. The 60 cycle signal is converted into a hum which is amplified, thereby distorting and degrading the quality of the musical sound.
The dual-coil, or "humbucking," pickup was developed to address this problem. One known arrangement is illustrated in U.S. Pat. No. 2,896,491, granted Jul. 28, 1959 to Lover. In the dual-coil arrangement, two coils are disposed adjacent to each other out of phase such that the 60 cycle currents produced in the coils by the interfering sources cancel one another out. This may be accomplished through reversing the winding direction of the second coil, or more usually accomplished with the two coils wound in the same direction, but connected out of phase. As a result, the audible hum is eliminated. However, this arrangement has two disadvantages of its own.
First, the introduction of a second coil increases the overall resistance, impedance, and inductance of the pickup. This results in a lower sensitivity to the vibrations of the strings and a weaker signal due to the loss of higher frequencies. Second, the dual-coil arrangement senses vibrations of each string at two relatively widely spaced points along the string, causing unnatural reinforcement and cancellation of certain harmonic frequencies other than the 60 cycle hum frequency generated by the vibrating strings. As a result, musical sound quality is degraded.
A number of solutions have been suggested for eliminating the second problem. These have included mounting the coils one on top of the other, using different diameter or gauge wire on each coil, and constructing the pickup so that the pole pieces are vertically offset. These methods, while addressing the frequency cancellation and reinforcement problem to differing degrees, do not affect the problem of additional resistance, impedance, and inductance introduced by the second coil. It is a primary objective of the present invention to provide an electromagnetic pickup that solves both problems.